Secretory proteins are often robust markers of changes in disease-relevant cellular states including ER stress and metastasis. The absence of technologies for detecting specific luminal secretory proteins in live cells represents a major gap in cell imaging tools. Our goal is to develop and deliver highly sensitive reporters that can detec differences in the expression of diagnostic secretory proteins within a population of live cells. T do this, we will combine three existing technologies to create a new class of imaging tools, STABs (Secretory Targeting Aptamer Beacons). More specifically, by combining modified bacterial toxins with nuclease stabilized aptamer beacons specific for secreted proteins such as VEGF or the UPR-induced endoplasmic reticulum proteins Ero1 and ERdj4, we aim to generate reagents which, when added directly to cells or tissues, will enter the secretory pathway and report the presence of these proteins. Theoretically, up to four distinct fluorescent dyes can be paired with unique aptamers to report on the expression of four different secretory proteins. We envision the probe technology will have utility for basic research and rapid clinical analysis of tissue samples.